This invention relates generally to micro-electromechanical systems (MEMS), and more specifically, to suppression of unwanted frequencies generated during operation of MEMS devices.
Micro-electromechanical systems (MEMS) integrate electrical and mechanical components on the same substrate, for example, a silicon substrate, using microfabrication technologies. The electrical components are fabricated using integrated circuit processes, while the mechanical components are fabricated using micromachining processes that are compatible with the integrated circuit processes. This combination makes it possible to fabricate an entire system on a chip using standard manufacturing processes.
One common application of MEMS devices is in the design and manufacture of sensor devices. The mechanical portion of the sensor device provides the sensing capability, while the electrical portion of the sensor device processes the information received from the mechanical portion. One example of a MEMS device is a gyroscope. Some inertial measurement units (IMUs) incorporate one or more MEMS gyroscopes.
One known type of MEMS gyroscope uses vibrating elements to sense angular rate through the detection of a Coriolis acceleration. The vibrating elements are put into oscillatory motion in a drive plane, which is parallel to the substrate. Once the vibrating elements are put in motion, the gyroscope is capable of detecting angular rates induced by the substrate being rotated about an input plane, which is perpendicular to the substrate. Coriolis acceleration occurs in a sense plane, which is perpendicular to both the drive plane and the input plane. The Coriolis acceleration produces a Coriolis motion having an amplitude proportional to the angular rate of the substrate. However, the vibrating elements sometimes exhibit other oscillatory movements outside of the above described and desired motion. These other oscillations are sometimes referred to as common mode oscillations, and can cause undesired outputs.
In one aspect, a method for reducing effects of common mode oscillations between two respective proof masses in micro-electromechanical systems (MEMS) devices is provided. The MEMS devices include a motor pickoff comb, a sense plate, and a motor drive comb for each proof mass. The method comprises amplifying signals received from respective motor pickoff combs, inverting the amplified signal from one of the motor pickoff combs, and generating a difference signal between the inverted, amplified signal from one pickoff comb, and the non-inverted, amplified signal from the other pickoff comb. The provided method also comprises inputting the difference signal into a control loop and generating motor drive signals for respective motor drive combs with the control loop.
In another aspect, a micro-electromechanical systems (MEMS) device is provided which comprises a substrate, a plurality of motor drive combs attached to the substrate, and a plurality of motor pickoff combs attached to the substrate, the MEMS device further comprises a plurality of proof masses, each proof mass suspended above the substrate and between one of the motor drive combs and one of the motor pickoff combs and a circuit configured to generate motor drive signals for the motor drive combs. The circuit is configured to receive signals from the motor pickoff combs, generate a difference signal between the signals received from the motor pickoff combs, and utilize the difference signal to control amplitude and pulse shape of the motor drive signals to suppress common mode oscillation in the proof masses.
In still another aspect, a circuit for suppressing common mode oscillations in a micro-electromechanical systems (MEMS) device is provided. The circuit comprises an amplifier circuit configured to generate a difference signal from motor pickoff signals received from motor pickoff combs of the MEMS device, and a control loop configured to receive the difference signal from the amplifier circuit. The control loop is configured to control amplitude and pulse shape of motor drive signals output to the MEMS device at least partially based on the difference signal received.
In yet another aspect, a method for suppressing common mode oscillations between proof masses in micro-electromechanical systems (MEMS) devices is provided. The MEMS devices include motor drive combs and motor pickoff combs. The method comprises receiving motor pickoff signals from motor pickoff combs, generating a difference signal from the received motor pickoff signals, and controlling pulse shapes of motor drive signals applied to motor drive combs based upon the difference signal.
In still yet another aspect, a micro-electromechanical systems gyroscope configured to suppress common mode oscillation is provided. The gyroscope comprises a substrate, a plurality of motor drive combs attached to the substrate, a plurality of motor pickoff combs attached to the substrate, and a plurality of proof masses, each proof mass suspended above the substrate and between one of the motor drive combs and one of the motor pickoff combs. The gyroscope further comprises an amplifier circuit configured to receive signals from the motor pickoff combs, and generate a difference signal between the signals received from the motor pickoff combs, and a control loop configured to utilize the difference signal to control amplitude and pulse shape of motor drive signals output to the motor drive combs to suppress common mode oscillation in the proof masses.